1、Designation: G 165 99 (Reapproved 2005)Standard Practice forDetermining Rail-to-Earth Resistance1This standard is issued under the fixed designation G 165; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the procedures necessary to followfor measuring resistance-to-earth of the running rails which areused as the c
3、onductors for returning the train operating currentto the substation in electric mass transit systems.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns,
4、if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:G15 Terminology Relating to Corrosion and Corr
5、osionTesting23. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 cross bondinsulated copper cables that connectedbetween adjacent sections of track to ensure electrical conti-nuity between them.3.1.2 direct fixation fastenera device for fastening run-ning rails to their support st
6、ructures.3.1.3 impedance bonda device connected to running railsfor automatic train operations.3.1.4 The terminology used herein, if not specifically de-fined otherwise, shall be in accordance with Terminology G15.Definitions provided herein, and not given in TerminologyG15, are limited to this prac
7、tice.4. Significance and Use4.1 Low resistance between the rails and earth could resultin large magnitudes of stray earth currents with the attendantcorrosion damage to underground metallic structures.4.2 These measurements are of a low voltage type and arenot designed to evaluate the high voltage d
8、ielectric character-istics of the rail insulating elements.4.3 Sections of track with rail-to-earth resistances less thanacceptable minimums must be tested in greater detail todetermine the reason(s) for this condition. Determination of thereason(s) for any low rail-to-earth resistance may require t
9、heuse of special testing techniques or special instruments, orboth, beyond the scope of this practice.4.4 The electrical tests call for the use of electric meters thathave varying characteristics depending on cost, manufacture,and generic type. It is assumed that any person employing thetest procedu
10、res contained herein will know how to determineand apply proper correction factors and that they will havesufficient knowledge to ensure reasonable accuracy in the dataobtained.4.5 This practice does not encompass all possible fieldconditions to obtain rail-to-earth resistance characteristics. Nogen
11、eral set of test procedures will be applicable to all situa-tions.5. Equipment5.1 Indicating dc; high impedance (minimum ten megohm)voltmeter (two required); multi-scale, capable of reading posi-tive and negative values without removing test leads; andcovering at least the following full scale range
12、s:5.1.1 0 to 10 mV,5.1.2 0 to 100 mV,5.1.3 0 to 1 V,5.1.4 0 to 10 V, and5.1.5 0 to 100 V.5.1.6 Meters shall be accurate within 1 % of full scale.5.2 Direct current ammeter, multi-scale, covering the fol-lowing full scale ranges:5.2.1 0 to 1 A,5.2.2 0 to 10 A, and5.2.3 0 to 100 A.1This practice is un
13、der the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.10 on Corrosion inSoils.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1999. Last previous edition approved in 1999 as G 165 99.2For referenced ASTM
14、standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohock
15、en, PA 19428-2959, United States.5.3 Direct current milliammeter, multi-scale, covering thefollowing full scale ranges:5.3.1 0 to 15 mA,5.3.2 0 to 150 mA, and5.3.3 0 to 1500 mA,5.4 An alternative to the ammeter and milliammeter is amillivolt meter and external shunts covering the listed currentrange
16、s. Meters (and shunt combinations if used) shall beaccurate to within 1 % of full scale.5.5 Direct current power source with control circuits. Gen-erally, 6 or 12 V automotive type wet cell batteries will suffice.5.6 Test wires, assorted lengths and sizes, to suit fieldconditions. Wires should have
17、minimum 600 V insulation inperfect condition (no visible cuts or abrasions) and be multi-strand copper conductors for flexibility.5.7 Miscellaneous tools as required for making wire con-nections, splicing, and so forth.5.8 Vehicle to transport equipment and personnel alongtrack to facilitate testing
18、.6. Visual Inspection6.1 The track section to be tested should be visuallyexamined to ensure the insulating components have beeninstalled and there is no debris, water, or other conductivematerial in electrical contact with the metallic track compo-nents that could result in the lowering of the effe
19、ctive track-to-earth resistance thus producing incorrect data.7. Electrical Tests7.1 Electrically isolate sections of track (see typical arrange-ments in Figs. 1 and 2). Length of track section to be tested isdependent upon the locations of rail insulators. Rail insulatorsare found at the ends of tu
20、rnouts and single and doublecrossovers. The lengths of the track sections will vary withinthe general range of 60 to 2750 m (200 to 9000 ft).7.1.1 Remove cable connections from across rail insulators.7.1.2 Disconnect cross bonds within section of track beingtested and other track.7.1.3 Disconnect po
21、wer traction substation negative feedercables from track section being tested.NOTE 1Switches within substation can be opened.7.2 Ensure electrical continuity between the rails within theinsulated track section being tested by the use of the existingcables at impedance bonds or by installing temporar
22、y wireconnections between the rails.7.3 Track-to-earth resistance measurements will be obtainedas shown on Fig. 3 for main track sections and as shown onFig. 4 for main track sections containing double crossovers.Measurements on track sections containing turnouts and singlecrossovers will be similar
23、 to that shown on Fig. 4 with thenumber of test points being determined by the electricalconfiguration of insulating joints and bonding cables.7.4 The track-to-earth resistance measurements for the trackin the train storage yards will require special consideration foreach section to be tested becaus
24、e of the number and location ofinsulating joints resulting from the type of signal system beingused within the yard area and because of the number of crossbonds and other bonding cables used within the yard.7.5 All data shall be recorded.7.6 A sketch showing location of the test and the electricalte
25、st set-up used shall be included.7.7 The number of readings taken to determine an electricalconstant or property must be sufficient to ensure that randomfactors due to human error in reading the instruments andtransient disturbances in the electrical network have negligibleinfluence on final results
26、. A minimum of three readings shouldbe obtained but additional readings may be required dependingupon the exact circumstances of the test. The adequacy of datagenerally can be established by the tester. Once the specifiedminimum number of readings have been obtained, data shouldbe examined to see th
27、at removal of neither the highest nor thelowest value will alter the arithmetic average of group by morethan 3 %. If the average is altered by more than 3 %, one morecomplete set of data should be taken and the results combinedwith the first set. If the test of the data still produces a changein the
28、 average value greater than 3 %, it may indicate anunstable condition in the system.7.8 Measurements Procedure(Fig. 3 for main tracksection, Fig. 4 for crossovers and turnouts).FIG. 1 Schematic Diagram Typical Mainline Track SectionG 165 99 (2005)27.8.1 Establish current circuit (I1).7.8.2 Establish
29、 rail-to-earth voltage (E1) measuring circuit.7.8.3 Obtain change in (E1) per ampere of test current (I1)(number of readings obtained to be in accordance with 7.7).7.8.4 Calculate the effective track-to-earth resistance, R1.1,(ohms) as change in (E1(volts) per ampere of (I1):R1.15delta E1delta I1(1)
30、7.8.4.1 With R1.1expressed in ohms, E1expressed in volts,and I1expressed in amperes.7.8.5 Obtain similar data for:R2.15delta E2delta I1(2)R3.15delta E3delta I1(3)R4.15delta E4delta I1(4)R4A.15delta E4Adelta I1crossovers and turnouts only! (5)7.8.6 Main Track Sections Only:7.8.6.1 Compare R2.1with R1
31、.1. R2.1should be equal to or nomore than 3 % less than R1.1. Greater variation could indicatethe test rail section is not effectively insulated from theadjacent section.7.8.6.2 Compare R4.1with R1.1. These values should beequal within about 3 %, with R4.1being less than R1.1. Morevariation than abo
32、ut 3 % could be indicative of attenuationresulting from the relationship of the resistance of the rail andthe track-to-earth resistance. A significant variation betweenR1.1and R4.1would be expected only in the event thetrack-to-earth resistance was much less than anticipated values.7.8.6.3 Compare R
33、3.1and R4.1. A variation of more thanabout 3 % could indicate that the track section under test is noteffectively insulated from the adjacent section.7.8.7 Crossovers and Turnouts OnlyCompare values ob-tained. All values should be within 3 % of each other becauseof the relatively short lengths of tr
34、ack involved. Any variationFIG. 2 Schematic Diagram Typical Double Crossover Track SectionNOTE 1All cable connections removed for measurements as shown on Fig. 1.NOTE 2Ground resistance to be on the order of 1/100 (or less) of the track-to-earth resistance for the section being tested.FIG. 3 Schemat
35、ic Diagram Mainline Test ArrangementG 165 99 (2005)3in the values obtained of greater than 3 % should be evaluated,to determine the reason(s) and what, if any, further action isrequired.NOTE 2Measurement of change in potentials across the insulatingjoints at all extremities are not required because
36、these measurements willbe obtained during tests on the adjacent track section.7.8.8 Compute the average resistance-to-earth of the testsection for 305 m (1000 ft) of track. The length (L) track mustinclude both main tracks plus crossover. (Thus a doublecrossover on 36 ft to 10 in. track centers woul
37、d contain in theorder of 366 m (1200 ft) of track.)RT5 R4.1x L305(6)where:RT= average resistance for 305 m (1000 ft)R4.1= track-to-earth resistance, V, andL = length of track within section, m.7.8.9 Record data.8. Acceptance Criteria8.1 Direct Fixation Track Construction:8.1.1 The track-to-earth res
38、istance for direct fixation track isgoverned by the electrical resistance associated with the directfixation rail fasteners and the number of fasteners.8.1.2 Under ideal conditions where there are no conductivematerials in electrical contact with the metallic rail or fastenercomponents, or both, tha
39、t contact the minimum electricalresistance through a direct fixation rail fastener is typicallyspecified as 100 megohms (108V).8.1.3 Spacing of the direct fixation rail fasteners on maintrack is typically 762 mm (30 in.). At this spacing there will be800 direct fixation rail fasteners in 305 m (1000
40、 ft) of maintrack.8.1.4 The minimum track-to-earth resistance for 305 m can,therefore, be calculated by assuming each direct fixation railfastener has the minimum specified resistance (Rp) and usingthe number (N) of these fasteners in parallel between the railsand earth.RT5RpN100 3 1068005 1.25 3 10
41、55 125 000 V (7)where:RT= track to earth resistance for 305 m,Rp= resistance of one fastener, andN = number of fasteners in 305 m of track.8.1.4.1 It is anticipated the actual resistances will be lessthan their specified minimum under actual installed conditions.Acceptance criteria will, therefore,
42、have to be based on anengineering evaluation of what can reasonably be anticipated.8.1.5 Any type of track that is constructed with dielectricisolators may be evaluated in a similar manner as describedabove with adjustment for the expected electrical resistance ofthe fastener.8.2 Wooden Tie Track Co
43、nstructions:8.2.1 The track-to-earth resistances for wooden tie construc-tion depends on several factors, the major ones being theresistivity of the wooden ties, the drainage characteristics ofthe road bed, and the spacing of the ties.8.2.2 The resistivity of the wooden ties depends on themoisture c
44、ontent of the wood. At low moisture content (lessthan 10 %) the wood is a moderately good insulator, butdecreases rapidly in effectiveness as the moisture content rises.8.2.3 The condition of the ballast and the road bed ingeneral to provide good water drainage and prevent theaccumulation of dirt, d
45、ebris, and other materials that canprovide an electrically conductive path between the rails andground.8.2.4 The spacing between ties is typically 686 mm (27 in.)on the main track and 762 mm (30 in.) on yard and secondarytrack.8.2.5 The acceptable criteria for track-to-earth resistancesmust be based
46、 on an engineering evaluation of what isreasonable for the specified construction and an evaluation ofwhat can be expected in magnitudes of stray earth currentsunder these conditions.8.3 Wooden Tie and Direct Fixation Construction in OneTest Section:NOTE 1All cable connections removed for measuremen
47、ts as shown on Fig. 2.NOTE 2Ground resistance to be on the order of 1/100 (or less) of the track-to-earth resistance for the section being tested.FIG. 4 Schematic Diagram Double Crossover Test ArrangementG 165 99 (2005)48.3.1 The track-to-earth resistance for each type of construc-tion within the te
48、st section can be calculated from the length oftrack of each type. These resistances can then be combined bylaws of parallel resistances to determine the theoretical value orcomparison with the measured value.1R51RA11RB11RC1.(8)where:R = combined resistance of all parallel com-ponents, V, andRA,RB,R
49、C. = resistances of the individual resistance tobe put in parallel, V.8.3.2 The anticipated resistances for direct fixation andwooden tie construction must be based on an engineeringevaluation of what is reasonable for the specified constructionand an evaluation of what can be expected in magnitudes ofstray earth currents under these conditions.8.4 Embedded Track ConstructionThe track-to-earth re-sistance for embedded track is governed by the electricalresistance associated with the track fastening system and thespecific material that is in contact with the r
